1. Technical Field
The embodiments herein generally related to wireless communications, and, more particularly, to Orthogonal Frequency Domain Multiplexing (OFDM) based communication systems.
2. Description of the Related Art
Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system. Each signal travels within its own unique frequency range (carrier), which is modulated by the data (text, voice, video, etc.). An OFDM spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” in this technique which prevents the demodulators from “seeing” frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to radio frequency (RF) interference, and lower multi-path distortion. This is useful because in a typical terrestrial broadcasting scenario there are multi path-channels (i.e., the transmitted signal arrives at the receiver using various paths of different length).
In a typical OFDM based communication system, pilot tones are inserted in the frequency domain scattered among the data tones. A receiver makes use of these pilot tones to estimate the channel on each frequency bin. The received data on each frequency bin are then divided by the estimated channel on the respective bins to obtain the transmitted information data. This process is usually called frequency domain equalization in OFDM based communication systems.
The channel estimation process based on the pilots tones are usually achieved through interpolation operations. The interpolating function usually takes the form of a finite impulse response (FIR) filter. The FIR filter needs to be chosen such that the original channel frequency response can be reconstructed. As the interpolation base points which are usually chosen to be the estimated channels on the pilot bins are noisy, the FIR filter interpolated channels at all other data bins are also noisy. The noisy channel estimates lead to noisy information data after the frequency domain equalization. This results in degraded carrier-to-noise (C/N) performance in OFDM based communication systems.